I also think these are Marin Lite brakes.
I've had four or five frames powder coated so far, but only steel ones. Aluminium is definitely not a problem, though. The coater I always go to works for several bike manufacturers and always has aluminium frames hanging there.
It's important to tape up all the bearing seats and mounting points well, then you won't have any problems. However, the coater should do this carefully. You can also tape up the frame number; with aluminium, this isn't a problem if it's not coated afterwards.
The powder coater I go to does the decals as well, as you need special heat-resistant films if you want them under clear coat. This costs a little extra, but it looks great and is incredibly robust.
A complete frame with pre-treatment, paint, decals and clear lacquer costs around €250. At a paint shop, you pay at least three times as much, as it involves much more work.
I think it would look really sick with that yellow and black parts
Awesome story so far!